Resistance welding



4 Sheets-Sheet 1 A. B. WHITE ETAL RESISTANCE WELDING Filed March 21, 1942 INVENTORS lyrea E h/bi/e and Ch$r/e s bC/m/ %ATTORN March 20, 1945 WITNESSES: 44%

March 20, 1945. w n- ETAL 2,372,147

RES ISTANCE WELDING Filed March 21, 1942 4 Sheets-Sheet 3 WITNESSES! v v INVENTQRS Q Y g g/red? 3/711: and S ar/es 60/2/2295. {Q )3 M Y ATTORQ Y March 20, 1945 A. 8., WHITE ETAL RES ISTANCE WELDING Filedlarch 21, 1942 4 Sheets-Sheet 4 A- 599 An h- AA 1 v r W W W WITNESSE S:

RTTORNE Pmmea Mar. 20,1945

RESISTANCE WELDING Alfred B. White and Charles H. Jennings, Forest Hills, Pa., assignors to Westinghouse Electric- & Manufacturing Company, East Pittsburg Pa., a corporation of Pennsylvania Application March 21, 1942, Serial No. 435,607v

(Cl. 2l9-10) 2 Claims.

Our invention relates, generally, to welding and it has reference, in particular, to methods of interrupted resistance welding.

Generally stated, it is an object of our invention to provide a new and novel method of resistance welding using repeated impulses of current having relatively high frequency characteristics.

More specifically, it is an object of our invention toprovide for charging a condenser from a relatively low frequency source and discharging the condenser into a welding circuit having a relatively high natural frequency so as to produce a plurality of interrupted current impulses having relatively steep wave fronts for effecting fusion of the members to be welded at each weld point.

A further object of our invention is to provide for resistance welding metallic members by using periodic relatively high frequency current impulses.

Another object of the invention is to utilize the skin effect of relatively steep wave front current impulses to distribute the flow of weld current about the periphery of the weld point.

It i also an important object of our invention to provide for applying successive impulses of welding current at spaced intervals of time to a weld point and utilizing current impulses having sufllciently steep wave fronts that the skin effect provides a ringlike weld in which the zone of fusion is substantially adjacent the outer edge thereof.

We also propose to provide for effecting successive high frequency discharges at spaced intervals of time through members to be welded by initiating said discharges at substantially corresponding points in different half cycles of the voltage wave of a relatively low frequency source and making the duration of such discharges less than a half cycle of the said wave.

It is also an object of our invention to provide for passing periodic relatively high frequency current impulses through members to be welded in synchronism with the voltage wave of a relatively low frequency source.

ing certain periods at spaced intervals of time and discharging it following each charging period into the primary circuit of a-welding transformer which, in connection with the condenser,

has a relatively high natural frequency, so that relatively high frequency current impulses of weld current may be produced in the welding circuit having a duration considerably less than the charging periods, whereby they occur at spaced intervals of time. Because of the skin effect of these relatively steep wave front im pulses, which causes successive impulses of such nature to crowd to'the periphery of the conduct-- ing path between the members to be welded, a different current distribution is produced in the weld zone. Welds may be thus produced between the members which have a much higher strength adjacent the periphery thereof, than welds produced in the conventional manner using impulses of a relatively low frequency.

For a more complete understanding of the nature and scope of our invention reference may be had to the following detailed description which may be read in conjunction with the accompanying drawings in which:

Figure 1 is a diagrammatic view of a resistance welding system for practicing our invention;

Fig. 2 is a'diagrammatic view of a synchronous interrupted spot welding system whereby the invention may be practiced;

Fig. 3' is a diagrammatic view of a, synchronous pulsation spot welding system whereby the invention may be practiced:

Figs. 4- and 5 illustrate voltage and current curves typical of the system shown in Fig. 1;

Figs. 6 and '1 illustrate voltage and current curves typical of the system shown in Fig. 2;

Figs. 8 and 9 illustrate voltage and current curves typical of the welding system of Fig. 3; and

Fig. 10 is a cross-sectional view of members being welded in accordance with-the invention In practicing our invention greatly improved welds may be made between metals which are usually diillcult to weld, such as, for example, copper and aluminum by using successive periodic impulses of welding current at each weld point which impulses have relatively high frequency characteristics-relatively steep wave fronts.

' One method of producing such impulses is by illustrating the current paths through the members.

Referring to Fig. 1, the reference numeral ll denotes, generally, a non-synchronous resistance welding system which may be used to practice the method of our invention. In this system a V condenser II and a suitable current controlling impedance I! are disposed to be connected to a source of alternating current I! by switch means 44, which may be either manually operated or t operated under the control of .timing means indicated generally by the numeral II, as shown.

charging a condenser from a suitable ource dur- The impedance I! may comprise an iron core reactance as shown or an air core reactance may be usedinstead, when the condenser it has a relatively large capacity. Switching means it is provided for connecting the primary winding ll of a welding transformer 88 across the condenser H.' llhe secondary winding IQ of the welding transformer may be connected to welding electrodes which engage the members it and 22 which are to be welded.

The timing circuit is may be of any suitable type comprising, for example, a condenser discharge tirning circuit such as is described in detail in Patent No. 2,008,4l3,'issued to John W. Dawson on July 16, 1935. The operation of the control switch it which connects the condenser i H to the source is for charging may be controlled by controlling the energization of the operating winding 23 thereof from a secondary section 2 5 of a control transformer 25 by means of a gaseous discharge valve 25 having a cathode 27, an anode 28 and a control grid 29. 30 may be provided, which may be normally connected in series circuit relation with the control grid 29 and the cathode 27! across sections BE, 32 and 33 of the secondary winding of the control transformer 25, the primary winding 35 ofwhich may be connected to the source 83.

In order to provide for controlling the conductivity of the valve 26, a control switch 36 may be provided for reversing the connections of the condenser 30 to the control grid 29 and cathode 28 to render the valve conductive. In order to initiate an operation a push button switch 38 may be provided for connecting the operating winding 33 of the control switch at to the section 2d of the control transformer secondary winding. A plurality of discharge resistors (it, d2, l3 and 44 of different values and an associated contact arm 55 may be provided for completing a discharge circuit for the timing condenser 38 so as to efiect timed discharges thereof and thus render the control valve 26 conductive for predetermined intervals of time.

The switching means it may be of any suitable type, comprising, for example, a switching system such as is described in detail in the copending application of Joseph Slepian and Alfred B. White, Serial No. 399,084, filed June 21, 1941. For example, the switching means it may comprise a pair of inversely connected arc discharge devices 68 and 49 having anodes 5B,mercury pool cathodes 5i and control electrodes 52. Control valves 53 and 5 3 having anodes 55, cathodes 56 and control grids 5? may be connected between the anodes and control electrodes of the are discharge devices 48 and 59, respectively, for controlling the conductivity of said devices.

In order to control the conductivity of the gaseous discharge valves 53 and 54, means may be provided for applying to the control grids 51 thereof suitable control voltages. For example, a control transformer 68 may be provided, having a primary winding 6| connected to the source I3 and secondary windings 62 and 63 which may 'be connected between the control grids 51 and thecathodes 56 of the controlvvalves 53 and 56 so as to apply to the control grids alternating current bias voltages which are negative with respect to the anode-cathode voltages of the control valves, and which render the control valves non-conductors until predetermined points in the source voltage wave.

In order to provide for rendering the arc discharge devices 48 and 49 conductive in response to the relatively high frequency currents pro- A timing condenser y duced in the welding circuit when the condenser H is connected thereto, means such as the control condenser so may be provided. The condenser 641 may, for example, be connected by movable contact members 65 and 66 to the grid resistors fil' and 68 which may be connectedln the grid circuits of the valves 53 and 5d, respectively. A gap device 69 may be connected between the control grids of the valves 53 and to to protect the valves against over voltage by providing a relatively low resistance breakdown path in case of too high a voltage in the grid circuit.

When the push button 38 is closed, the control relay 3G operates to connect the timing condenser 30 between the control grid 29 and the cathode 27 of the control valve 2s, so as to apply a positive bias voltage to the control grid is and render the control valve conductive. The operating winding 23 of the control switch is thereby energized, causing closure of the main contacts Mic, and connecting the condenser ii to the source 63.

Referring to Figs. 4 and 5 as well as Fig. i, it will be seen that when the switch it, closes the condenser is connected to the source 83 and com nences to charge. When the voltage of the condenser ll-indicated by the dotted curve areaches a'given value in a half cycle of the source voltage wave-indicated by the curve b, and the negative bias voltage-indicated by the dot and dash curve 0 on the control grids 51 reaches a sufficiently low negative value, one or another of the control valves 53 or 54 will be rendered conductive, depending on the polarity of the particular half cycle. Itsassociated arc discharge device is thereby rendered conductive, connecting the primary winding ll of the welding transformer 98 across the condenser it. As the natural frequency of the condenser H and the primary winding is relatively high, the wave front of the current impulses through the primary winding will be relatively steep, as shown by the curves d of Fig. 5, shown as oscillatory, it will be understood. that they may also be limited to single unidirectional discharges, either by critically damping the discharge circuit, or providing a unidirectional bypass therefor to absorb reverse oscillations, ii? desired.

In the circuit shown the condenser 6% connected between the grid circuits of the control valves 53 and 551 provides a relatively low resistance path to current impulses having relatively steep wave fronts, so that the other of the control valves is rendered conductive in response to the reverse vggage produced across the condenser H by the initialdischarge through the primary winding of the welding transformer. The other of the arc discharge devices is thereby rendered conductive during the same initial half cycle of the relatively low frequency source I3, permitting the condenser l I to discharge in. the opposite direction through the primary winding II. This sequence may be continued several times during an interval of less duration than one-half cycle of the source voltage wave, thus producing a surge of welding current having a relatively high peak value and comprising one or more relatively steep front waves which surge or impulse lasts during aninterval which is less than one half cycle of the source voltage wave.

As soon as the voltage of the condenser ll reaches a predetermined minimum value, the arc discharge devices 48 and 49 are rendered non- While these impulses are- II reaches a predetermined value of the opposite polarity on the next succeeding half-cycle of the source voltage wave, the arc discharge devices 40 and 40 are again rendered conductive to effect the flow of subsequent relatively high frequency current impulses through the members to be welded. Successive impulses will be produced so long as the switch I4 is closed, which in this instance is determined by the timing means I5.

Since these relatively high frequency impulses are not initiated until substantially corresponding predetermined poinm in different half cycles of the voltage wave of .the source ,preferably near to the zero value thereof, and each is of shorter duration than one half cycle of the source voltage wave, so that it terminates before the next succeeding one, intervals of time occur between successive impulse surges of welding cur rent, and interrupted pulsations of welding current are produced which may be utilized in welding according to our invention. The surfaces of the members being welded are thus provided with cooling periods between successive impulses or surges of weld current. Due to the high fre quency characteristics of these impulses, the flow rendering the control valve conductive in timed relation to the ilow of current through the inductance I2.

Means may be provided for normally rendering the control valve 02 non-conductive, such as the grid transformer 00 which may be connected to the source I3 and may be provided with a rectifier device 89 and condenser I00 connected across the secondary winding IOI thereof for producing a negative bias voltage across the control resistor I02 in the circuit of the control grid 00 of the control valve 02 to normally render said control valve non-conductive.

In order to render the control valve 02 conductive in predetermined relation to the voltage wave of the source I3 and for predetermined time intervals thereof, the voltage applied to the con trol grid 00 of the control valve 82 may b controlled by means such asthe timing valve I03 having an anode I00, cathode I05 and a control grid I00 under the control of a timing condenser I01 and a sequence control relay I08. The control relay I00 may be provided with normally closed contact members l00a and I00c' for normally connecting the timing condenser I01 to the secondary winding N0 of a control transformer I II through the timing valve I03 for charging.

Means such as the control switch H0, may be provided for connecting the operating winding Ill of the control relay I00 to the source II to effect operation of the relay. Contact members I089, f and It may be arranged to close first, connecting the grid transformer 03 across the imare substantially ringlike in form, and members thus welded are more diillcult to separate after thus welding. 7

Referring to Fig. 2, the reference numeral 10 denotes; generally, a synchronous resistance welding system whereby the improved method of welding may be practiced. As shown in this figure, the condenser II and the impedance I2 may be connected to the alternating-current source I0 insynchronism therewith by switching means 10 under the'control of timing means indicated generally by the numeral 15. The primary winding I1 of a welding transformer l0 may be connected to the condenser It under predetermined voltage conditions thereof in a manner similar to that describedin connection with Fig. 1 by similar switching means indicated generally by the numeral IS.

The switching means 10 may,. for example,

' comprise arc discharge devices 11 and 10 connected inversely in" series circuit relation with the condenser II, impedance I2 and source ll. The are discharge devices 11 and 10 may be of the usual type, havinganodes 10, cathodes 00 and control'electrodes 0|. Control valves "and 03 having anodes ,cathodes 00 and control grids 0 may be connected between the anodes and control electrodes of the arc discharge devices 11 and 10 for controlling the conductivity thereof.

In order to render the control valve 02 normally non-conductive, suitable means may be provided for applying a negative bias thereoi',-such as the control transformer 00. which may be connected to the source I0, and provided with a rectifier 00 and a condenser 00 for producing a negative bias voltage across a. control resistor SI in the grid circuit of the control valve 03 to provide a suitable negative bias voltage on the control grid 00 thereof.- Means such asthe grid transformer 02 having the primary winding 00 thereof connected across the condenser II and impedance I2, may

be provided for producing positive bias voltage for pedance I2, and connecting the control resistor I02 between the control grid and cathode of the timing valve I03 so as to apply a negative bias to the control electrode thereof rendering the valve non-conductive. Contact vmembers 1001) close subsequently connecting the timing condenser I01 in series circuit relation with the timing valve I03, discharge resistors H0 and H0, and a bias discharge resistor III which is connected in the grid circuit of the control valve 02 through the contact members l00d.

In order to provide for rendering the timing valve conductive at a predetermined point in the voltage wave of the source I3, means such as the impulse transformer H8 may be provided, having a primary winding II! connected to the source'li through a phase shifting circuit I20, and a secondary winding I2I connected across a control resistor I22 in the grid circuit of the timing valve I00. When the timing condenser I01 is connected in serie circuit relation with the timing valve I03, the negative bias across the control resistor I 02 is sufllcient to retain the timing valve non-conductive. After the closure of contact members i00e which close last, a relatively sharp voltage impulse is produced across the control resistor I02 in the grid circuit by the impulse transformer Ill rendering the timing valve conductive. The duration of the period of conductivity is controlled by the rate of discharge of the condenser I01 through the control resistors H5 and 0.

During the interval in which the condenser I01 discharges through the timing valve I02 and the control resistors II! and H0, a positive bias is applied to the control grid 00 of the control valve 02 through the control resistors IIS' and III, sufficient to overcome the negativebias from the control resistor I02 to render the valve 02 1 lit welding transformer lit to the condenser ill for efiecting the passage of periodic relatively high frequency weld current impulses through the members to be welded in timed relation to the source frequency is efiected in the anner de scribed in connection with the welding system oi Fig. 1, during the period determined by the dis= charge time of the condenser till.

Referring to Figs. 6 and 7 of the drawings, it

will be seen that a plurality of periodic Weld cur rent impulses indicated by the curves c may be produced by the discharges of the condenser ldll. These impulses are in timed relation to the voltage wave 1 of the source it and occur whenever the negative bias voltage 9 applied to the control grids 57 reaches a predetermined minimum value relative to the condenser voltage wave it. As the impulses are of relatively high frequency, several oscillations may occurduring an interval which is less than a single 'hali cycle of the source frequency. These impulses may have relatively high peak values and are of relatively short duration in comparison with a half cycle of the source frequency. Intervals thus occur between the high frequency discharges of successive half cycles of the source frequency, independently of any timing means and interrupted weld current impulses are produced which tend to concentrate about the periphery oi the weld zone, producing a weld of high peripheral strength.

' Referring to Fig. 3, the reference numeral 6% denotes, generally, a pulsation resistance welding system for producing repeated periodic impulsesv of relatively high frequency welding current for welding in accordance with our invention. In this system, the primary winding it or the welding transformer it may be connected to the con-= denser M by switching means it in the same manner shown and described in connection with the system of Fig. l. The reference numeral i843 may denote generally switching means for con trolling the connection of the condenser ii to the source It under the control of timing means indicated generally by the numeral lid for re peated timed intervals at predetermined spaced intervals of time in synchronism with the source The switching means 836 may comprise gener ally arc discharge devices ltd and it? having anodes I38, cathode 539 and control electrodes ME. The discharge devices use and it? may be connected inversely in a manner well known in the art and connected in series circuit relation with the condenser ii, impedance i2 andthe source 83. Gaseous discharge valves M2 and i413 having anodes ld l. cathodes M5 and control grids 966 may be provided for controlling the conductivity of the discharge valves 536 and i377 in the usual manner, being, for example, connected between the anodes and control electrodes thereof.

A control transformer Hit having a rectifier device 9 and a condenser ltd connected thereacross may be provided for applying a'negative 5 which may be energized from the source la aevaiev bias voltage to the control electrode Mt of the control valve I 33 for normally rendering the con.- trol valve M3 non-conductive. Suitable means may be provided for rendering the control valve the conductive in predetermined timed relation to the current wave of the source it, such as, for example, the'grid transformer i52, connected across the charging circuit of the condenser E 5. Thus when the condenser is charged during a half cycle the impulse produced by the grid transformer 552 renders the control valve 853 conductive in predetermined time relation to the succeeding half cycle of the source current wave.

The timing means l35 for controlling the conductivity of the control valve 552 may be generally similar to that described in detail in the copending application Serial No. 271,951, of Firm H. Gulliksen, filed May 5, 1939 and now Patent No. 2303353, dated December -l, i942. For example,

the control grid 5 35 of the control valve 32 may be connected through an. on timing resistor 356 to an intermediate tap 553 of a voltage divider through a transformer Hi5 and a rectifying device ltd. The cathode'l ifi of the control valve M2 may be connected to a more positive intermediate tap it? of the voltage divider 85% so as to normally render the control valve M2 nonconductive.

in order to render the control valve it? conductive for predetermined intervals of time, suitable on" timing means indicated generally by the numeral lfiil may be provided. Suitable oft timing means indicated generally by the numeral ldi may be provided for periodically rendering the on timing means ineffective. The on" timing means may, for example, comprise a pair of discharge devices m2 and Edit connected in series circuit relation with the on timing resistor I5! between the positive terminal ltd oi the voltage divider Md and the intermediate tap $53. The discharge device Hi2 may be of the high vacuum type which is normally conductive and may be rendered non-conductive by applying a negative impulse to, the control electrode M55 thereof. The discharge device 363 may be of the arc-like type which may be normally maintained non-conductive by means of a negative bias voltage applied to the control electrode its thereof from the voltage divider 54 and the oil timing control resistor $65, and may be rendered conductive by means of a control impulse applied thereto from the secondary winding iii? of an impulse transformer lit energized from. the source it. An on timing condenser 563 may be connected across the "on timing resistor l5! and provided with a control resistor ltd. A control valve lid may be connected across the condenser ltd in series circuit relation with the primarywinding ill of a, control transformer H2 having a secondary winding connected he tween the cathode and control grid ltd of the discharge device 332, for rendering said discharge device non-conductive when the condenser reaches a predetermined voltage at which it is dischargedthrough the control valve till. An additional secondary winding lit may be provided for applying a control impulse to a con trol valve lid. of the arc-like type which may be connected in series circuit relation with a second control valve N5 of the high vacuum type in the OE timing circuit for connecting the oii timing resistor I66 across a portion or the voltage divider 454 between the intermediate taps H8 and I'll. An ofi" timing condenser winding of a control transformer I8I to produce a negative bias impulse in the secondary winding I82 to render the high vacuum control valve I non-conductive, and disconnect the of! timing resistor I66 from the voltage divider I64, terminating the "of!" time period. An ad- [ditional secondary winding I83 applies an impulse to a "stop" condenser I86 through a rectifler I86.

When the control valves I62 and I63 of the on timing circuit I60 are conductive, a positive bias voltage is produced in the "on timing resistor I6I which overcomes the negative bias produced in the grid circuit of the control valve I42 from the voltage divider I54, and renders the control valve I42 conductive. The discharge device I36 is thus rendered conductive for positive half cycles of the source I3 and the condenser II is connected to the source for charging. Discharge of the condenser through the switch means I6 occurs in the manner described in detail in connection with the welding system of Fig. l The impulse of current through the impedance I2 in charging the condenser on a positive half cycle produces a control voltage in the grid circuit of the control valve I43 through the grid transformer I62 which renders the discharge device I31 conductive for the succeeding negative half cycle of the source I3 thus charging the condenser II in the opposite direction.

The control valve I42 is periodically rendered conductive on successive positive half cycles of the source I3 during an interval determined by by the charging time of the on'timing condenser I64. When the condenser I64 discharges through the control valve I18 rendering the control valve I62 non-conductive and rendering the control valve I14 of the "o timing circuit conductive, the control valve I42 of the arc discharge v device I36 is rendered non-conductive. The ilow of current through the "off timing resistor I66 and the control valves I14 and I13 of the "off timing circuit from the voltage divider I54 produces a sufhcient negative bias in the grid circult of the control valve I63 of the on timing circuit to maintain it non-conductive. The control valves I14 and I15 of the off" timing circuit remain conductive until the off timin condenser I18 reaches a predetermined voltage whereupon it is discharged through its associated control valve I80 and control impulses are produced in the secondary winding of the control transformer III to render the control valve I16 non-conductive terminating the off period and to add an increment of charge to. the stop" timing condenser I86. Upon the next succeeding impulse from the secondary winding I61 of the impulse transformer I28, the control valves I62 and I63 of the "on" timing circuit are again rendered conductive for a predetermined interval or time and the arc discharge devices I36 and I31 are accordingly rendered conductive to charge the condenser II on succeeding half cycles of the source I3.

The '.on" timing and of! timing circuits continue to conduct alternately until the stop time condenser I86 receives a predetermined charge whereupon the "stop valve I81 is rendered conductive, connecting the 011" timing resistor I68 to the voltage divider I64 and producing a negative bias voltage which renders the on timing circuit non-conductive, preventing further welding operations until subsequent opening and closure of the control switch I88 which controls theenergization of the control relay I89 which controls the connection of the on and off" timing circuits to the voltage divider I54.

In practicing our invention with a circuit such as shown in Fig. 3, periodic impulses of relatively high frequency current having relatively steep wave fronts may be produced for timed periods which are spaced at predetermined time intervals determined by the relatively low frequency source I3, as shown in Figs. 8 and 9, wherein m denotes the relatively high frequency steep wave front weld current impulses, timed relative to the voltage curve n of the source I3. The timing thereof may be varied relative to the source voltage wave by varying the amplitude of the negative biasvoltage' 0 relative to the value of the condenser voltage wave p. Accordingly, successive impulses of relatively high frequency current may be applied to the members to be welded at spaced intervals of time, so as to permit cooling of the surfaces therebetween by conductivity of the heat from the surfaces through the electrode members as well as during the off intervals.

Not only are the advantages of pulsation welding as thus obtained in all the methods of practicing our invention hereinbefore described, but in addition, the skin effect of the relatively high frequency, or relatively steep wave front current impulses, may be utilized to produce a concentration of the weld current about the periphery of the weld spot in the manner illustrated in Fig. 10. As shown therein, the lines extending between the electrodes indicate typical current paths through the weld members. These paths instead of crowding to the center of the initial point of fusion between the members, crowd about the periphery. Welds are thus produced which are ringlike, having a relatively high strength about the periphery. Such welds are materially stronger and are more able to resist forces tending to separate the members.

From the above description and the accompanying drawings, it will be realized that we have provided an improved method of welding which is simple and effective, and which utilizes not only the principles of pulsation welding wherein timed intervals are provided between repeated impulses of weld current to permit at least partial cooling of the member being welded at the surface thereof, but further utilizes the advantages of relatively high frequency or steep wave front impulses, so that the current distribution in the weld zone is such that a concentration of current occurs about the periphery of the weld. Welds may thus be produced wherein the heating effect is localized at the contact surfaces between the members, so that the depth of the fusion and heating effected zones are considerably less. The high frequency, high current imcal weld spot of approximately $4, inch diameter may be increased approximately four times, result in substantially Wing" welds, as the con-= centration of weld current about the periphery of the weld is appreciable, causing a crowding of the current ,to the periphery and a marked increase in the strength or the peripheral weld zone.

Since certain changes may be made in the above description and difierent embodiments of the invention may be made without departing from the spirit thereof, it is intended that all the matter contained in the above description or shown in the accompanying drawings shall be considered as illustrative and not in a limiting sense,

claim as our invention:

is The method of resistance welding electri= cally conductive p which comprises to weld spots by subjecting each spot to successive pulses oi welding current at timed intervals, each of said pulses being of greater than one=half cycle of a 69 cycle source and comprising a plurality of discrete high frequency impulses, each of said impulses having a duration of less than one half cycle of a-Gil cycle source with each of said impulses occurring in successive half cycle of a fill-cycle source and consisting or at least one complete cycle of thehigh frequency.

2. A method of interrupted resistance welding metal parts which comprises, producing ringshaped welds therebetween by subjecting the parts at each weld zone to successive timed pulses of current at predetermined timed intervals, each i pulse being of greater duration than one-half cycle of a 60 cycle source and consisting of a plurality of discrete impulses of relatively high frequency each having a duration less than one half cycle of a relatively low frequency wave with each of said impulses occurring in successive half cycles of said wave so as to be spaced less than at one half cycle intervals oi said low frequency and consisting of at least one cycle of the high frequency.

ALFRED B. Wlll'lE.

CHARLES H. JENNHIGS. 

